filer: optimization for leveldb, add leveldb2

large filer db may see high CPU and disk usage due to background compaction

weed/command/scaffold.go

@@ -63,6 +63,12 @@ enabled = false
 
 [leveldb]
 # local on disk, mostly for simple single-machine setup, fairly scalable
+enabled = false
+dir = "."					# directory to store level db files
+
+[leveldb2]
+# local on disk, mostly for simple single-machine setup, fairly scalable
+# faster than previous leveldb, recommended.
 enabled = true
 dir = "."					# directory to store level db files